Research Progress on Hydrophone Elements and Their Applications in Towed Line Arrays and Imaging Sonar for Underwater Detection

Driven by growing marine exploitation and maritime security demands, underwater detection systems impose stringent performance requirements for deep-sea early warning, seabed resource exploration and underwater infrastructure inspection. This review surveys recent advances in key underwater detection hardware. In terms of hydrophone technologies, this review elaborates the developmental landscape and landmark innovations of piezoelectric, fiber-optic, and micro-electromechanical-system (MEMS) hydrophones. Regarding array architectures, it dissects the core engineering bottlenecks and state-of-the-art evolutionary trends for two representative underwater detection arrays: towed line arrays and imaging sonar. Unresolved technical challenges and prospective research directions are summarized, aiming to provide actionable references for researchers engaged in the design and field deployment of underwater detection hardware and algorithms.